The present invention relates to fusing members and, more specifically, the present invention relates to fuser member coatings comprising functional release agents that, for example, enhance release of toner from a fuser roll in an electrostatographic, especially xerographic, machine. In embodiments, the release agents of the present invention are comprised of a hydride (SiH) functional silicone oil that prevents offset by providing a coating on a fuser roll substrate, which preferably has an outer layer of a high temperature resistant polymer and in embodiments, a fluoropolymer. In embodiments, the coating reacts with a conductive filler which is present on the polymer surface layer of the fuser roll. Advantages of the fuser members of the present invention include, in embodiments, reduction in toner offset, providing lower surface energy of the outer fusing layers, providing a more uniform coating of fusing oil on the fusing surface layer, decreasing the amount of wax needed in toners, increasing fuser release life, and rapid diffusion of the fuser oil into the copy sheet, thereby reducing or alleviating the problems of poor fix of certain inks such as magnetic inks and reducing or eliminating poor adhesion of binding glues and attachable notes such as 3-M Post-It.RTM. notes. In embodiments, the release coatings of the present invention can be obtained by combining a hydride functional siloxane with active functional groups on filler components thereby providing a low surface energy silicone surface over the filler. The fuser members of the present invention including the fuser oils herein, which can be selected for a number of known electrophotographic imaging and printing processes, possess a number of advantages as indicated herein.
In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member, and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles and pigment particles, or toner. The visible toner image is then in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support which may be the photosensitive member itself or other support sheet such as plain paper.
The use of thermal energy for fixing toner images onto a support member is well known. To fuse electroscopic toner material onto a support surface permanently by heat, it is usually necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to be firmly bonded to the support.
Typically, the thermoplastic resin particles are fused to the substrate by heating to a temperature of between about 90.degree. C. to about 200.degree. C. or higher depending upon the softening range of the particular resin used in the toner. It may be undesirable, however, to increase the temperature of the substrate substantially higher than about 250.degree. C. because of the tendency of the substrate to discolor or convert into fire at such elevated temperatures, particularly when the substrate is paper.
Several approaches to thermal fusing of electroscopic toner images have been described. These methods include providing the application of heat and pressure substantially concurrently by various means, a roll pair maintained in pressure contact, a belt member in pressure contact with a roll, a belt member in pressure contact with a heater, and the like. Heat may be applied by heating one or both of the rolls, plate members, or belt members. The fusing of the toner particles takes place when the proper combination of heat, pressure and contact time are provided. The balancing of these parameters to bring about the fusing of the toner particles is well known in the art, and can be adjusted to suit particular machines or process conditions.
During operation of a fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support are passed through a nip formed between the roll pair, or plate or belt members. The concurrent transfer of heat and the application of pressure in the nip affects the fusing of the toner image onto the support. It is important in the fusing process that no offset of the toner particles from the support to the fuser member take place during normal operations. Toner particles offset onto the fuser member may subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thus increasing the background or interfering with the material being copied there. The referred to "hot offset" occurs when the temperature of the toner is increased to a point where the toner particles liquefy and a splitting of the molten toner takes place during the fusing operation with a portion remaining on the fuser member. The hot offset temperature or degradation of the hot offset temperature is a measure of the release property of the fuser roll, and accordingly it is desired to provide a fusing surface which has a low surface energy to provide the necessary release. To ensure and maintain good release properties of the fuser roll, it has become customary to apply release agents to the fuser roll during the fusing operation. Typically, these materials are applied as thin films of, for example, silicone oils or amino oils, to prevent toner offset.
U.S. Pat. No. 4,257,699 to Lentz, the subject matter of which is hereby incorporated by reference in its entirety, discloses a fuser member comprising at least one outer layer of an elastomer containing a metal-containing filler and use of a polymeric release agent.
U.S. Pat. No. 4,264,181 to Lentz et al., the subject matter of which is hereby incorporated by reference in its entirety, discloses a fuser member having an elastomer surface layer containing a metal-containing filler therein and use of a polymeric release agent.
U.S. Pat. No. 4,272,179 to Seanor, the subject matter of which is hereby incorporated by reference in its entirety, discloses a fuser member having an elastomer surface with a metal-containing filler therein and use of a mercapto-functional polyorganosiloxane release agent.
U.S. Pat. No. 5,401,570 to Heeks et al., the subject matter of which is hereby incorporated by reference in its entirety, discloses a fuser member comprised of a substrate and thereover a silicone rubber surface layer containing a filler component, wherein the filler component is reacted with a silicone hydride release oil.
U.S. Pat. No. 4,515,884 to Field et al., the subject matter of which is hereby incorporated by reference in its entirety, discloses a fuser member having a silicone elastomer fusing surface which is coated with a toner release agent which includes an unblended polydimethyl siloxane.
U.S. Pat. No. 5,512,409 to Henry et al. teaches a method of fusing thermoplastic resin toner images to a substrate using amino functional silicone oil over a hydrofluoroelastomer fuser member.
U.S. Pat. No. 5,516,361 to Chow et al. teaches a fusing member having a thermally stable FKM hydrofluoroelastomer surface and having a polyorgano T-type amino functional oil release agent. The oil has predominantly monoamino functionality per active molecule to interact with the hydrofluoroelastomer surface.
The use of polymeric release agents having functional groups, which interact with a fuser member to form a thermally stable, renewable self-cleaning layer having good release properties for electroscopic thermoplastic resin toners, is described in U.S. Pat. Nos. 4,029,827; 4,101,686; and 4,185,140, the disclosures each of which are incorporated by reference herein in their entirety. Disclosed in U.S. Pat. No. 4,029,827 is the use of polyorganosiloxanes having mercapto functionality as release agents. U.S. Pat. Nos. 4,101,686 and 4,185,140 are directed to polymeric release agents having functional groups such as carboxy, hydroxy, epoxy, amino, isocyanate, thioether and mercapto groups as release fluids.
The preferred release agents for fuser members are silicone release oils and monoamino silicone release oils. However, depending on the type of outer layer of the fuser member chosen, there may be several drawbacks to using silicone or monoamino silicone oils as release agents.
With regard to known fuser coatings, silicone rubber has been the preferred outer layer for fuser members in electrostatographic machines. Silicone rubbers interact well with various types of fuser release agents. However, polyfluoroalkoxypolytetrafluoroethylene (PFA Teflon) used as an outer coating for fuser members is more durable and abrasion resistant than silicone rubber coatings. Also, the surface energy for PFA Teflon is lower than silicone rubber coatings.
With regard to known fusing oils, silicone oil has been the preferred release agent for PFA Teflon coatings for fuser members. However, release agents comprising silicone oil do not provide sufficient release properties for toner because the silicone oil does not wet fuser coatings of PFA Teflon. Therefore, a large amount (greater than 5 mg/copy) of silicone oil is required to obtain minimum release performance. Alternatively, a large amount of wax must be incorporated into the toner in order to provide adequate release of the toner from the fuser member.
For other fluoropolymer, and especially fluoroelastomer fuser member outer layers, monoamino silicone oil has been the release agent of choice. However, monoamino oil does not diffuse into paper products, but instead, reacts with the cellulose in the paper and therefore remains on the surface of the paper. It is believed that hydrogen bonding occurs between the amine groups in the monoamino oil and the cellulose hydroxy groups of the paper. Alternatively, the amine groups may hydrolyze the cellulose rings in the paper. The monoamino oil on the surface of the copied paper prevents the binding of glues and adhesives, including the attachable notes such as adhesive of 3-M Post-it.RTM. notes, to the surface of the copied paper. In addition, the monoamino silicone oil present on the surface of a copied paper prevents ink adhesion to the surface of the paper. This problem results in the poor fix of inks such as bank check endorser inks, and other similar inks.
Yet another drawback to use of monoamino silicone and silicone fuser release agents is that the release agents do not always react as well with conductive fillers which may be present in the fuser roll surface. It is desirable for the release agent to react with the fillers present on the outer surface of the fuser member in order to lower the surface area of the fillers. The result is that the conductive filler may be highly exposed on the surface of the fuser member, thereby resulting in increased surface energy of the exposed conductive filler which will cause toner to adhere to it. An increased surface energy, in turn, results in decrease in release, increase in toner offset, and shorter fusing release life.
Therefore, there exists a specific need for a fusing member release agent for use with a polymer, and more specifically a fluoropolymer, outer layer of a fuser member, wherein the release agent does not remain on the surface of the copy sheet. In addition, a specific need exists for a release agent useful in connection with conductive particle filled fluoropolymer outer surfaces of fuser members, wherein the release agent sufficiently reacts with the conductive filler on the outer surface of the fuser member, enabling a reduction in surface energy of the exposed conductive filler, which ultimately results in a decrease in toner offset and longer fuser release life. Moreover, a need exists for a fusing member release agent for use with a polymer outer layer of a fuser member, wherein the release agent which can be used in relatively small amounts and wherein the release agent does not require a relatively large amount of wax to be incorporated into the toner in order to be effective.